Assessment of uv pre treatment to reduce fouling of nf membranes by fiona_messe



                        Assessment of UV Pre-Treatment to
                         Reduce Fouling of NF Membranes
                                              Di Martino Patrick1, Houari Ahmed1,
                                            Heim Véronique2 and Marconnet Cyril3
                                                        1Laboratoire ERRMECe (EA1391),

                                      Institut des Matériaux, Université de Cergy-Pontoise
                                                         2Syndicat des Eaux d’Ile de France
                                             3Veolia Water, Compagnie Générale des Eaux,


1. Introduction
Nanofiltration (NF) is an efficient technology to produce safe and biologically stable
drinking water from surface water (Cyna et al. 2002). NF can respond to the increased
demand of water with higher quality due to the evolution of the legislation and of the
customer’s expectation. NF treatment allows the reduction of the concentration of organic
precursors to disinfection byproducts, and the reduction of the concentration of trace
contaminants such as pesticides and pharmaceuticals. The introduction of NF in the
drinking water production plant of Méry-sur-Oise, France, conducted to several changes in
quality of the distributed water: reduction of total organic carbon (TOC) and Biodegradable
dissolved organic carbon (BDOC) by a factor 3 to 5, reduction of THMs by a factor 2,
reduction of viable bacteria population by a factor 10, reduction of chlorine demand of the
distribution system by a factor 3, amount of pesticides below detection level.
Four membrane properties are important for the efficiency of a water treatment plant: high
rejection of dissolved organics, low salt rejection, low energy consumption, and stable
performance after repetitive cleanings. Membrane fouling generates flux decline leading to an
increase in production cost due to increased energy demand and chemical cleaning. Moreover,
fouling induces reduction in membrane life. Different types of NF fouling can be defined on
the basis of fouling material: inorganic fouling due to deposition on membrane surface of
inorganic scales; organic fouling due to humic acids, proteins and carbohydrates (natural
organic material, NOM); biofouling due to biofilm formation at the membrane surface.
Flux decline associated with NOM fouling and with biofouling can be partially restored by
chemical cleaning (Al-Amoudi et al. 2005, Di Martino et al. 2007, Houari et al. 2010,
Roudman et al. 2000). Biofouling is distinct from NOM fouling caused by contaminated
organic matter derived from biological systems (Flemming et al., 1997). Biofouling involves
biologically active microorganisms which grow at the membrane surface as complex
structures termed biofilms (Lappin-Scott et al. 1989). Biofilm formation precedes biofouling,
which becomes an issue only when biofilms reach thickness and surface coverage that cause
declined normalized flux and/or increase in normalized pressure drops during NF
operation (Vrouwenvelder et al., 1998, Ridgway, et al. 1996).
220                                                                Expanding Issues in Desalination

Fouling and subsequent chemical cleaning of nanofiltration membranes used in water
treatment are inevitable but can be decreased by adequate pretreatments (Al-Amoudi and
Lovitt 2007, Di Martino et al. 2007, Flemming et al. 1997, Hilal et al., 2004, Houari et al. 2010,
Speth et al. 2000). Pre-treatment must achieve a strong removal of microbial cells and
growth-promoting compounds from the feed water (Vrouwenvelder et al. 1998, Wend et al.
2003, Vrouwenvelder and Van der Kooij 2001, Marconnet et al. 2009). Several pre-treatments
schemes prior to NF have been evaluated including coagulation/precipitation, biofiltration,
granular activated carbon (GAC) adsorption, microfiltration/ultrafiltration, ozonation, pre-
chlorination, slow sand filtration, and UV irradiation (Cyna et al. 2002, Wend et al. 2003,
Vrouwenvelder et al. 1998, 2008, Speth et al. 2000, Koyuncu et al. 2006). UV pre-treatment
has several advantages: it has immediate germicidal effect; it is a closed and thus a safe
system that requires only a small space for equipment; it does not generate byproducts; it
acts only on water and cannot have deleterious effects on membranes. Nevertheless, since
UV disinfection has no residual effect, the time between the UV irradiation and the
membrane filtration has to be the shortest possible, so as to avoid bacterial regrowth
(Salcedo et al. 2007). Few studies have evaluated the benefit of using UV as a pre-treatment
upstream from NF and/or RO membranes (Conlon and Jhawar 1993, Koyunku et al. 2006,
Munshi et al. 2005, Mofidi et al. 2000).
In the present study, the addition of a UV irradiation process upstream from NF modules
was assessed to maintain membrane performances and to limit biofouling.

2. Materials and methods
2.1 Pilot units
Two identical nanofiltration pilot units (2 x 1 m3/h) containing each a single 4-inch spiral
wound NF element harbouring NF200B membranes (DOW Filmtec, Delft, The Netherlands)
were used (Figure 1). A UV pilot including a low pressure mercury vapour lamp
(monochromatic at 254 nm) was operated at a dose of 400 J/m2 upstream from one of the
pilots. The pilot units were fed by clarified river water pre-treated through sand filtration
(sand-filtered water, SFW). Pilot 1 was fed SFW while pilot 2 was fed SFW irradiated by UV
(SF + UVW), during a filtration run of 10 weeks (from February to May). Both NF pilots
included an internal pre-treatment step made of pH neutralisation, 20 and 6 µm cartridge
filtration and antiscalant injection, similar to what can be found in most of NF industrial
units. The role of this pre-treatment was to reduce scaling (pH neutralisation and antiscalant
addition) and particulate fouling (pre-filtration). A recycling loop enriches the module feed
water with concentrate at a ratio concentrate/feed of 70%, in order to accelerate fouling.

2.2 Water quality parameters
Total direct counts (TDC) of microbial cells after 4’,6-Diamino-2-phenyindole
dihydrochloride (DAPI) staining, and active bacteria counts (ABC) of microbial cells after
cyano 2-3 dytolyl – tetrazolium chloride (CTC) staining are determined by epifluorescence
microscopy. Dissolved Organic Carbon (DOC) is measured with a Total Carbon Analyzer
using persulfate oxidation of organic carbon, followed by infra-red non-dispersive detection
of the CO2 produced by the oxidation reaction. Biodegradable dissolved organic carbon
(BDOC) is determined by batch incubation with sand-fixed bacteria according to the
bioassay procedure developed by Joret and Lévi (1986) and the French standard XP T 90-
Assessment of UV Pre-Treatment to Reduce Fouling of NF Membranes                                                     221

                                                                                                940 L/h
                                                                                               R = 70%
                                                                                             NF membrane
                                                                                                module        Concentrate
                                                                  LP Pre -
                                                                                                                266 L/h
                                             Pilot 1                                    HP

                                                                     Acid                      134 L/h
                                         Feed water                Injection
                                          460 L/h
                                                                          injection           Recirculation
                                                                                                940 L/h
                                                                                               R = 70%
                                                                                             NF membrane
                                                                                                module        Concentrate
                                              Pilot 2             LP                                            266 L/h

                                                        UV irradiation   Pre -filters
                                                          400 J/m 2                            Permeate
 A                                   B                                                          134 L/h

Fig. 1. A, photograph of the nanofiltration pilot showing the membrane module, the pumps
and the electronic instrument panel. B, scheme of the experimental setup. Feed water was
sand-filtered water. LP, low pressure pump. HP, high pressure pump.

2.3 Modules performance monitoring
The performances of the membrane modules, water permeability (L. h-1. m-2. bar-1)
normalized at 25°C and corrected of the osmotic pressure, and longitudinal pressure drop
(LPD) also termed feed channel pressure drop (FCP) normalized by temperature and the
flow rate along the module, were monitored on-line during both filtration tests.

2.4 Membrane autopsy
NF modules from the two pilot units were autopsied at the end of the filtration test.
Membrane samples cut from randomly chosen areas of the module were air-dried and
analysed by Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR)
spectroscopy. Other membrane samples were fixed in paraformaldehyde before staining
and fluorescence microscopy analysis, as described below.

2.4.1 Dry weight, protein content, microbial activity and wettability of the deposit
A membrane coupon of 50 x 90 cm was gently scraped to collect the wet deposit. The
deposit was lyophilized, and the lyophilisate weight was measured. The lyophilisate was
then dissolved in ultrapure water, vortexed and sonicated.
The protein concentration was determined after centrifugation by Bradford’s colorimetric
assay (Biorad protein assay, Biorad laboratories GmbH, München, Germany), bovine serum
albumine (BSA, Sigma-Aldrich) being used as a standard (Bradford 1976).
For ATP assays, remnants of NF membrane (9.6 cm2 for each one) were cut. Each sample
was put in 3 mL of ultrapure water and sonicated (Branson sonifier 450). The concentration
of ATP released by microbial cells after sonication was measured by the luminescence
luciferine/luciferase test (ATP Determination Kit, Invitrogen). The intensity of light
produced by the reaction was measured with a luminometer (Sirius Luminometer, Berthold
222                                                             Expanding Issues in Desalination

detection systems GmbH, Pforzheim, Germany). The ATP quantity was calculated by
comparison with free ATP standards. The ATP concentration was an indicator of the
microbial activity within the deposit.
The wettability of the membrane surface was determined by measuring the water contact
angle of the foulant matter. A membrane coupon of 1 cm2 was cut. An ultrapure water drop
was deposited on the surface of the membrane, and the tangent angle between the drop and
the surface was measured with a drop shape analysis-profile device (DSA-P, Kruss, Germany).

2.4.2 Analysis of membrane foulants by ATR-FTIR
Samples of air-dried fouled membranes were analyzed by ATR-FTIR spectroscopy. IR
spectra were recorded using a Tensor 27 IR spectrophotometer with a 45° diamond/ZeSe
flat plate crystal and an average depth penetration of 2 µm. Each spectrum presented was
the result of 32 accumulations obtained with a resolution of 2 cm-1 with air as the
background. IR bands indicative of biomass were detected near 1650 cm-1 (amide I,
corresponding mainly to proteins), 1550 cm-1 (amide II, corresponding mainly to proteins),
1090 and 1040 cm-1 (corresponding mainly to polysaccharides) as previously defined
(Doumèche et al. 2007). The IR signal near 700 cm-1 was used to calculate ratios
corresponding to relative IR signals of biomass (amide I / membrane signal, amide II /
membrane signal, and band near 1040 cm-1 / membrane signal) (Houari et al. 2009). Mean
values ± standard deviation of relative IR signals of biomass are shown here.

2.4.3 DAPI and lectin staining of foulants
DAPI and lectin staining of foulants were done as previously described (Doumèche et al.
2007). Samples of the fouled membranes were treated with paraformaldehyde (4 %, v/v)
prior to lectin application in order to fix the foulant matter. Double staining with a mixture

agglutinin (LEA) (Sigma, Saint Quentin Fallavier, France) was done. 100 L of a mixture of
of TRITC-labelled peanut agglutinin (PNA) and FITC-labelled Lycopersicon esculentum

two lectins (final concentration of 100 g/mL each) were carefully applied directly on top of
the membrane. After incubation during 30 min in the dark at room temperature, unbound
lectins were removed by washing with filter-sterilized water. Following the lectin staining
step, the fouled membranes were treated with a solution of DAPI (1 mg/L) (Sigma, Saint
Quentin Fallavier, France) in filter-sterilized water. After incubation during 30 min in the
dark at room temperature, unbound DAPI was removed by washing the membrane surface
with filter-sterilized water. The stained preparations were then mounted with Mowiol
(Calbiochem, Meudon, France) and stored at 4°C in the dark. For the negative control, the
lectins and DAPI were replaced by filter-sterilized water.

2.4.4 Microscopy and image analysis
The fouled membranes stained with DAPI and fluorescently labelled lectins were examined
with a Leica epifluorescence microscope (MPS 60) and with a Leica SP2 upright confocal
laser scanning microscope (DM RAX-UV) equipped with the Acousto-Optical Beam Splitter
(AOBS) system and using 63X, N.A. 1.32, oil immersion objective (Leica microsystems,
Rueil-Malmaison, France). For epifluorescence images, DAPI was excited at 364 nm, CTC
was excited at 450 nm, FITC was excited at 494 nm, and TRITC was excited at 550 nm. For
confocal images, DAPI was excited at 405 nm and observed from 410 to 600 nm, FITC was
excited at 488 nm and observed from 505 to 540 nm, TRITC was excited at 543 nm and
Assessment of UV Pre-Treatment to Reduce Fouling of NF Membranes                           223

observed from 560 to 600 nm. The selection of spectral emission window for each
fluorophore has been determined through λ scan analysis on single stained membrane
fragments. The gain and offset for each photomultiplier have been adjusted to optimize
nucleic acid and lectins detection. Images of the Confocal Laser Scanning Microscopy
(CLSM) observations (1024×1024 pixels) have been acquired through a sequential mode,
between stacks, to exclude spectral crosstalk from the data. 400 Hz scan speed was used and
signal/noise ratio has been increased through frame average. Overlay and maximum
projection of the z-stacks files have been performed with post acquisition Leica confocal
software (LCS) functions to obtain the presenting snapshots. Original z-stack Leica files
have then been imported into Imaris 4.0 software (Bitplane AG, Zürich) to obtain snapshots
illustrating xz and yz representations.

2.5 Statistical analysis
ATP concentrations, contact angles measurements and values of relative IR signals of
biomass obtained with or without UV irradiation were compared by the equal-variance
Student’s t test, following the variance test with Fisher F statistics. P values below 0.05 are
considered significant.

3. Results
3.1 Feed water characterizations
Mean values of total direct bacteria counts (TDC), active bacteria counts (ABC), Dissolved
Organic Carbon (DOC) concentration and Biodegradable Dissolved Organic Carbon
(BDOC) concentration of the different feed waters are presented on Figure 2.

                       DAPI and CTC bacteria counts (log bact/mL)

                                                                    5            CTC
                               DOC and BDOC (mgC/L)

                                                                    4            BDOC




                                                                        SFW   SF+UVW
Fig. 2. Total direct Counts (DAPI) and active counts (CTC) of bacteria in feed waters,
concentration in of dissolved organic carbon (DOC) and biodegradable dissolved organic
carbon (BDOC) in the feed water with (SF + UVW) or without (SFW) UV irradiation.
224                                                                                                                                              Expanding Issues in Desalination

UV pre-treatment did not affect the organic carbon concentration, as it was applied with a
low pressure lamp at a reasonable dose of 400 J/m2. The germicide effect of UV pre-
treatment can be seen on the active bacteria counts (about 0.3 log removals).

3.2 Membrane performances
Water permeability and Longitudinal Pressure Drop (LPD) varied slightly all along the
filtration period (Fig. 3). At the end of the test, water permeability decreased by 2.5 % with
SFW as feed water and by 3.6 % with SF + UVW as feed water and the LPD value was 1.08
for SFW and 1.02 for SF+UVW. Both permeability and LPD evolutions were very low and
the differences between the two conditions were not significant.

                                    9                                                                                       1,4
Water permeability (L.h .m .bar )

                                                                                               Normalized longitudinal pressure



                                                                                                         drop (LPD)

                                                                             SFW                                            0,8                                           SFW
                                                                             SF+UVW                                                                                       SF+UVW
                                        A                                                                                              B
    3                                                                                                               0,6
 February 28                                    March 20           April 9    April29                              February 27               March 19           April 8   April 28

                                                           Dates                                                                                        Dates

Fig. 3. NF module water permeability (A) and longitudinal pressure drop (B) evolution during
filtration. Sand-filtered water with (SF + UVW) and without (SFW) UV pre-treatment.

3.3 Autopsy results: Characterization of the biofilm
3.3.1 Dry weight, protein content, microbial activity and wettability of the deposit
Table 1 gives mean values and standard deviations for the dry weight, protein content,
microbial activity (ATP concentration) and wettability of the deposit. Dry weight, protein
concentration and microbial activity of the membrane deposit were lowered after UV pre-
treatment indicating that UV pre-treatment limited noticeably the formation of the deposit on
NF membranes. The difference between the water contact angles of the module fed SFW and
the module fed SF + UVW was in concordance with the other data: UV pre-treatment lowered
the water contact angle; the membrane surface was more wettable. This may be linked to the
decrease of the quantity of exopolymeric substances covering the surface of the membrane;
therefore the water contact angle came closer to its initial low value (between 15 and 30°).

                                                 Parameter                              Unit                                               SFW                  SF + UVW
                                                 Dry weight                         µg/cm2                                               102.3                  40.7
                                            Protein concentration                   µg/cm2                                            1.15 ± 0.09            0.34 ± 0.03
                                             ATP concentration                     pmol/cm2                                           0.40 ± 0.18           0.16 ± 0.12**
                                             Water contact angle                    degrees                                           83.4 ± 7.6             74.7 ± 4.3*
Table 1. Characterization of the foulant matter deposited on NF modules during filtration. Sand-
filtered water with (SF + UVW) and without (SFW) UV pre-treatment. *, P < 0.05. **, P < 0.01.
Assessment of UV Pre-Treatment to Reduce Fouling of NF Membranes                                                   225

3.3.2 Analysis of membrane foulants by ATR-FTIR
IR spectra acquired on the surface of NF modules are presented on Figure 4.


                                                                                     Absorbance (arbitrary unit)



                2000       1800   1600   1400   1200   1000   800   600
                                  Wawenumber      [cm-1]

                                                                                     Absorbance (arbitrary unit)



                2000       1800   1600   1400   1200  1000    800   600
                                  Wawenumber      [cm-1]
                                                                                     Absorbance (arbitrary unit)




                 2000      1800   1600   1400   1200   1000   800   600
                                  Wawenumber      [cm-1]

Fig. 4. IR spectra of the foulant matter deposited on NF modules. A, Sand-Filtered water
(SFW) without UV pre-treatment. B, Sand-Filtered water with UV pre-treatment (SF +
UVW). C, virgin membrane.
226                                                              Expanding Issues in Desalination

Different spectra illustrating heterogeneity among the foulant layer are presented for each
fouled membrane. Signals corresponding to the presence of proteins (signal at 1650 cm-1)
and exopolysaccharides (signal at 1040 cm-1) were observed on the two modules. Many IR
bands corresponding to the membrane were detected for all the spectra, indicating only
partial coverage of the membranes by the fouling layer. The membrane IR signal near 700
cm–1 was used to calculate relative ratios for the proteins and polysaccharides signals to
compare semi-quantitatively the abundance of exopolymers on the different NF elements.
Table 2 indicates the mean values and standard deviations of these ratios.

            Relative IR signal ratios                SFW                 SF + UVW
           Amide (I) /  membranea                 0.87 ± 0.22           0.74 ± 0.25**
        Polysaccharides / membraneb               0.52 ± 0.22           0.44 ± 0.29*
Table 2. Relative IR signals measured at the surface of NF modules. Sand-filtered (SF)-
water, with (SF + UVW) and without (SFW) UV pre-treatment. a, Amide (I) / membrane is
the ratio of signal intensities at 1650 cm-1 and 700 cm-1. b, Polysaccharides / membrane is the
ratio of signal intensities at 1040 cm-1 and 700 cm-1. *, P < 0.05. **, P < 0.01.
The relative signal of amide (I), characterizing the amount of proteins, and the signal near
1040 cm-1, revealing the amount of polysaccharides, were significantly lowered for UV pre-
treated waters. FTIR-ATR spectroscopy showed that the exopolymers amount on the
membrane surface was decreased when the feed water was UV-irradiated.

3.3.3 Microscopy
Microscopic observations made on NF membrane surfaces are illustrated on Figures 5 and
6. Each micrograph presented corresponds to one area of the corresponding membrane
after the observation of at least 5 distinct areas at a magnification of x400 and 10 distinct
areas at a magnification of x630 randomly distributed at the membrane surface. The
snapshots presented on Figure 6 illustrations are showing the tendency of the fouling
The analysis of the foulant matter after DAPI staining showed that the membrane surface
was colonized by many microorganisms organized as microcolonies (Figure 5). Lectin
staining revealed the presence of exopolysaccharides on the surface, with a highly
heterogeneous repartition. Some areas of the membrane surface were covered by
important amounts of microorganisms and polysaccharides, while others were still virgin
and did not present any microbial cells (Figure 5 and 6). Microorganisms and
exopolysaccharides were organized as a biofilm highly structured in three dimensions
clusters. The most intense signal for membranes fed SFW or SF + UVW was obtained with
the LEA-FITC lectin.
The cell concentration on the surface of the membrane was decreased when the feed water
was UV-irradiated (SF + UVW). DAPI total direct counts indicate a bacteria concentration
of 1.07 ± 0.4 x 106 cells/cm2 with SF + UVW as feed water and 2.20 ± 1.17 x 106 cells/cm2
with SFW as feed water. As illustrated on Figures 5 and 6, the amount of polysaccharides
on the surface appeared to be lower after UV irradiation. Moreover, UV irradiation
seemed to increase the heterogeneity of the deposit: the distinction between colonized
areas and virgin areas, already visible with SFW as feed water, is yet stronger with SF +
Assessment of UV Pre-Treatment to Reduce Fouling of NF Membranes                      227

                       SFW                               SF + UVW
           DAPI                                  DAPI

           PNA                                   PNA

           LEA                                   LEA

Fig. 5. Interactions between fluorescently-labelled lectins and fouled membranes, as
visualized by epifluorescence microscopy. Sand-filtered (SF)- water, with (SF + UVW) and
without (SFW) UV pre-treatment. PNA, TRITC-labelled peanut agglutinin. LEA, FITC-
labelled Lycopersicon esculentum agglutinin. Magnification, x 630.
228                                                             Expanding Issues in Desalination

Fig. 6. Interactions between fluorescently-labelled lectins and fouled membranes, as
visualized by CLSM. A, sand-filtered water without UV pre-treatment (SFW). B, sand-
filtered water with UV pre-treatment (SF + UVW). Colour allocation: blue - DAPI, green -
FITC-labelled Lycopersicon esculentum agglutinin (LEA), and red - TRITC-labelled peanut
agglutinin (PNA). Magnification, x 630. Black arrows indicate the orientation of the foulant
matter from the top to the bottom.

4. Discussion
The goal of this work was to study the influence of a UV irradiation pre-treatment located
upstream from nanofiltration modules, on the biofouling of NF membranes at a pilot scale.
The efficiency of UV pre-treatment to control biofouling was assessed with feed water
obtained after coagulation/sedimentation/sand filtration.
We first measured the effects of UV irradiation on feed water parameters. UV pretreatment
had no effect on the concentration of available dissolved carbonic microbial nutrients, since
the DOC and BDOC concentrations were not modified by irradiation. UV treatment with a
Assessment of UV Pre-Treatment to Reduce Fouling of NF Membranes                           229

low pressure mercury lamp (UV intensity varying from 10 mWs cm-2 to 240 mWs cm-2) has
been shown to be able to induce the decomposition of humic substances (Li et al. 1996, Lund
et al. 1994). These effects of UV irradiation on humic acids have been observed for DOC
concentrations of at least 15 mg C/L. The apparent discrepancy between the present results
and the literature may be related to the relatively low concentrations of DOC and BDOC in
the feed water in our experiments (less than 4 mg C/L). In the present study, UV irradiation
decreased bacterial viable counts by 0.3 log. This may be related to the well-established
mechanism of UV disinfection, i.e. bactericidal and bacteriostatic effect of UV mainly
through genetic damages induction (Gaid et al. 2006, Al-Adhami et al. 2007). This effect of
UV irradiation can be potentialized by other pretreatments decreasing BDOC like
ozonation/GAC adsorption since dissolved organic matters are necessary to repair cell
damages (Alkan et al. 2007, Camper 2004).
The second part of this work measured the effects of UV irradiation on the fouling of NF
membranes, i.e. evolution of the filtration performances and formation of the deposit at the
membrane surface. The analysis of the foulant matter by complementary technical tools
showed that UV pre-treatment decreased the deposit formation. The global quantity of
foulant matter and all the biofilm parameters measured were decreased when UV pre-
treatment was applied: the total direct bacteria counts, viable bacteria counts, microbial
activity (ATP concentration), and the concentration of exopolymeric substances (proteins
and polysaccharides) were reduced at the membrane surface after UV irradiation.
Nevertheless, UV pre-treatment did not modify the evolution of the permeability and of the
longitudinal pressure drop. This may be linked to the short duration (10 weeks) of the test.
Biofouling of nanofiltration membranes has been associated with a LPD-increase (Characklis
and Marshall 1990, Vrouwenvelder et al., 2000, 2008) and/or a permeability decrease (Speth
et al., 2000, Marconnet et al. 2009; Vrouwenvelder et al., 1998, 2009). Water permeability is a
physical parameter which is related mainly to the material structure, to the porosity of the
deposit, to its wettability, and to a lesser extent to its global quantity (Herzberg and
Elimelech 2007). We did not observe any relation between membrane surface wettability
and membrane permeability. Despite different evolutions of the membrane surface
wettability of the two modules, the water permeability was the same.
On the whole, this work shows that controlling the concentration of active bacteria in the
feed water is efficient to reduce deposit, biomass and biopolymer accumulation on the
membrane surface. In this study, the 0.3 log removal of planktonic bacteria induced by UV
irradiation is strong enough to decrease significantly the biofilm growth on the surface of
the membrane but not fouling, i.e. filtration performances decrease. A longer duration test
may be necessary to obtain higher biofilm development at the membrane surface with
effects on membrane performances, i.e. permeability decrease and longitudinal pressure
drop increase.

5. Conclusion
UV irradiation used as a pre-treatment upstream from nanofiltration is able to:
-   lower the concentration of viable planktonic bacteria in the feed water.
-   reduce the global quantity of deposit, the sessile bacteria concentration and the amount
    of extracellular polymeric substances present on the surface of the membrane.
UV pre-treatment, by limiting biofilm development at the membrane surface during
nanofiltration of surface water, may be able to control the membrane performances decrease
230                                                             Expanding Issues in Desalination

observed during long term operation. New experiments with longer filtration duration tests
are needed to demonstrate that UV irradiation can help to maintain membrane
performances as well as to limit biofilm growth at the NF membrane surface.

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                                      Expanding Issues in Desalination
                                      Edited by Prof. Robert Y. Ning

                                      ISBN 978-953-307-624-9
                                      Hard cover, 412 pages
                                      Publisher InTech
                                      Published online 22, September, 2011
                                      Published in print edition September, 2011

For this book, the term “desalinationâ€​ is used in the broadest sense of the removal of dissolved,
suspended, visible and invisible impurities in seawater, brackish water and wastewater, to make them
drinkable, or pure enough for industrial applications like in the processes for the production of steam, power,
pharmaceuticals and microelectronics, or simply for discharge back into the environment. This book is a
companion volume to “Desalination, Trends and Technologiesâ€​, INTECH, 2011, expanding on the
extension of seawater desalination to brackish and wastewater desalination applications, and associated
technical issues. For students and workers in the field of desalination, this book provides a summary of key
concepts and keywords with which detailed information may be gathered through internet search engines.
Papers and reviews collected in this volume covers the spectrum of topics on the desalination of water, too
broad to delve into in depth. The literature citations in these papers serve to fill in gaps in the coverage of this
book. Contributions to the knowledge-base of desalination is expected to continue to grow exponentially in the
coming years.

How to reference
In order to correctly reference this scholarly work, feel free to copy and paste the following:

Di Martino Patrick, Houari Ahmed, Heim Véronique and Marconnet Cyril (2011). Assessment of UV Pre-
Treatment to Reduce Fouling of NF Membranes, Expanding Issues in Desalination, Prof. Robert Y. Ning (Ed.),
ISBN: 978-953-307-624-9, InTech, Available from:

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